# Need help with magnetic pulsing

1. Mar 12, 2009

### bryand2

I have designed a magnetic pulser using a camera flash and a copper wire air core inductor wired in series with the flash. when the flash is discharged, some of the energy in the capacitor is dumped through the coil creating a moving magnetic field. My problem is im not sure how much gauss it is creating. I took it to school and used a gauss meter in the physics lab, it only read about 120 gauss, now i dont know what kind of gauss meter it was or wether it was set to the right setting. I need to create between 20,000 and 40,000 gauss. When i place a key ring in the middle of the coil and discharge the flash it launches the key ring about 5 feet into the air but I dont know if thats means anything, any help would be greatly appreciated

2. Mar 13, 2009

### Bob S

Measuring magnetic fields (especially transient ac fields) without the proper equipment) is difficult. You first need to use engineering formulas to calculate the inductance L of the air coil (see http://www.coilws.com/c_winding_main/Air Coil Inductors.pdf). Then, assuming the inductance L and the energy storage capacitor C form a relatively hi-Q (low series resistance) circuit, and all (most) of the energy stored in the capacitor flows into the inductance, use energy conservation to calculate the peak current in the coil:

(1/2) L I2 = (1/2) C V2, where L is in Henrys and C in Farads.

Finally, the peak field in the coil (long solenoid) is given by

B = 4 pi 10-7 NI where I is peak amps, N is turns per meter and B is in Tesla (1 Tesla = 10,000 Gauss).
I hope this helps.